Quartz glass has a low coefficient of thermal expansion (CTE) and thus has characteristics such that it is excellent in thermal shock resistance and also excellent in chemical durability and mechanical properties. Heretofore, as a material capable of absorbing or radiating infrared light while having such characteristics of quartz glass, one so-called black colored quartz glass or black quartz glass (hereinafter generally referred to as “black quartz glass”) has been available which contains a transition metal such as vanadium or niobium. In view of the infrared absorptivity and thermal shock resistance, such black quartz glass has been used as a component material of a product for high precision analysis, such as optical analytical instruments or infrared heating apparatuses.
Further, silica glass containing TiO2 (hereinafter referred to as TiO2—SiO2 glass) is known to be a very low thermal expansion material having a coefficient of thermal expansion (CTE) smaller than quartz glass, and the coefficient of thermal expansion can be controlled by the TiO2 content in the glass, whereby it is possible to obtain a zero expansion glass having a coefficient of thermal expansion being close to zero. Accordingly, if such silica glass containing TiO2 being a very low thermal expansion material, has infrared absorptivity, it can be used as e.g. a cell material for optical analytical instruments or a component material of infrared heating apparatuses, which is superior in thermal shock resistance, etc., to conventional black quartz.
A conventional method for preparing TiO2—SiO2 glass is as follows. First, a silica precursor and a titania precursor are, respectively, converted into a vapor form, and then mixed. Such a vapor form mixture is feeded into a burner and thermally decomposed to form TiO2—SiO2 glass particles. Such TiO2—SiO2 glass particles will be deposited in a refractory container and at the same time will be melted to form TiO2—SiO2 glass. However, in TiO2—SiO2 glass prepared by this method, the temperature region where the coefficient of thermal expansion becomes substantially zero, is limited to about room temperature.
Further, U.S. Pat. Application Publication No. 2002/157421 discloses a method which comprises forming a TiO2—SiO2 porous glass body, converting it to a glass body, and then obtaining a mask substrate therefrom.
conventional black quartz glass has a coefficient of thermal expansion which is equal to or more than quartz glass, and thus, its thermal expansion coefficient is substantially large. Thus, black quartz glass which has been used for a conventional cell material for optical analysis or for a component material of infrared heating apparatuses, has been inadequate in thermal shock resistance, as its thermal expansion coefficient is large.